P.E.I.'s newest senator is shaping up to also be the Island's most expensive.

During his first three months in the red chamber, Conservative Senator Mike Duffy racked up more than $100,848 in travel and office expenses, more than double the average of what the other three Island senators spend in a typical quarter.

Duffy's rate of spending puts him in the top rank of senatorial expenses. An NDP-produced report showed the top spender for the 2008-09 year was Mobina Jaffer, a Liberal senator for British Columbia, at $323,173. Sustained over a year, Duffy's expenses would come in at $403,392.

Duffy's expenditures have been the focus of attention since NDP MP Peter Stoffer raised them last week. Stoffer said the expenses are a reason his party believes Canada's senate is a waste of taxpayer money. Stoffer and Duffy later got into a bit of a shouting match about the issue on CBC's Power and Politics with Evan Solomon.

"We also mentioned Liberals as well," Stoffer said, in defence of his party's focus on Duffy.

"Did you mention Roméo Dallaire, did you mention Sharon Carstairs?" Duffy shot back. "This is in the Commons public accounts committee and it's a scam."

Duffy made the point that his expenses are similar to Stoffer's, but the Nova Scotia MP said there's a difference in their jobs.

"I'm responsible to 91,000 people in the riding of Sackville-Eastern Shore. He's responsible to the prime minister of Canada, and that's it," Stoffer told CBC News on Tuesday.

"When you don't have a constituency and you're nominated or appointed by the prime minister, you get to travel the country to do the prime minister's bidding. I don't think tax dollars, money, should be going in that particular route."

Stoffer said he was trying to show how the 27 senators appointed by Prime Minister Stephen Harper over the past year could end up costing Canadian taxpayers $177 million.

Duffy did not return calls from the CBC on Tuesday.